The invention relates to detection of contaminants in containers, particularly contaminants whose presence is manifested by foam or bubbles.
The popularity of refillable containers has increased as the costs, both social and financial, associated with disposal of packaging have become less acceptable. For example, in many countries, water and other beverages are sold in refillable bottles. These bottles are often made from a type of plastic known as polyethylene terephthalate.
After use, refillable containers are returned to a bottling plant where they are cleaned and inspected before being refilled. For example, machine vision inspection of clean, dry, empty bottles is often used in the bottling industry to inspect for mechanical defects in the bottles, such as incorrect overall dimensions, breaks, cracks, and scratches. The inspection process, in addition to checking for physical damage such as cracks, must screen the containers to eliminate those that include contaminants that might degrade the flavor, safety, or other qualities of the product that they contain. The risk of contamination is greater when a container is made from plastic, as opposed to glass, because some contaminants can be absorbed into the plastic walls of the container. Absorbed contaminants can persist despite cleaning procedures, and can later leach into the product.
As used herein, "contaminant" means any substance that can be detected in a container by the detection system of the invention and whose presence is incompatible with the product with which the container is to be filled. For example, detergents are contaminants with respect to beverage containers, and flavored beverages may be contaminants with respect to bottled water.
As also used herein, "turbid contaminant" means a contaminant the presence of which in or with a liquid results in the liquid and contaminant mixture being turbid or unclear so as to scatter radiant energy directed into the liquid and contaminant mixture. Similarly, "foaming contaminant" means a contaminant the presence of which in or with a liquid results in the liquid and contaminant mixture producing foam or bubbles on, at or below the surface of the liquid when agitated. Where the context so indicates, the definition of "liquid" includes a liquid and contaminant mixture.
Though some contaminants, such as detergents and fabric softeners, are visibly colored and can be detected by human inspectors, such human visual inspection is undesirable when bottles or other containers are moving on high speed conveyors and stopping or touching the bottles to perform an inspection is undesirable or overly expensive. Moreover, such human visual inspection is subject to lapses in attention by the inspectors.